We present a device-independent analysis of controlled quantum teleportation where the receiver is not trusted. We show that the notion of genuine tripartite nonlocality allows us to certify control power in such a scenario. By considering a specific adversarial attack strategy on a device characterized by depolarizing noise, we find that control power is a monotonically increasing function of genuine tripartite nonlocality. These results are relevant for building practical quantum communication networks and also shed light on the role of nonlocality in multipartite quantum information processing.
We present a device-independent analysis of controlled quantum teleportation where the receiver is not trusted. We show that the notion of genuine tripartite nonlocality allows us to certify control power in such a scenario. By considering a specific adversarial attack strategy on a device characterized by depolarizing noise, we find that control power is a monotonically increasing function of genuine tripartite nonlocality. These results are relevant for building practical quantum communication networks and also shed light on the role of nonlocality in multipartite quantum information processing.
Controlled quantum gate teleportation (CQGT) enables controller-regulated quantum gate transmission in distributed networks. The current CQGT scheme faces security challenges as both genuine tripartite entanglement and insecure classical-quantum hybrid resources can achieve high standard metrics (fidelity or control power). In this paper, we propose a device-independent (DI) CQGT verification scheme using genuine tripartite nonlocality in black-box scenarios. In the quantum cnot gate teleportation, our DI verification scheme based on Svetlichny inequality achieved the maximum inequality violation, which is superior to the traditional Clauser-Horne-Shimony-Holt (CHSH) type scheme. It is crucial that we establish a direct relationship between Svetlichny inequality violation and the effective control power (ECP) of the controller in eavesdropping depolarization channels, where ECP corresponds to the maximum inequality violation. This work addresses critical security verification gaps in CQGT protocols while highlighting the fundamental role of multipartite nonlocality in quantum information processing.
Quantum nonlocality is an important resource for ensuring the security of quantum communication, which plays an indispensable role in building quantum networks. From bipartite to multipartite quantum systems, various inequalities are constructed as tools to unearth the quantum nonlocality. Control power is a crucial indicator for evaluating supervision, control, and collaboration in quantum networks. However, there is currently no exploration of the relevance between the control power and the quantum nonlocality in continuous variable quantum networks. In this work, based on the Mermin−Klyshko (MK) inequality with rotated quantum-number parity operators, we reveal the quantum nonlocality of general Greenberger−Horne−Zeilinger-type (GHZ-type) entangled coherent states, which can be extended to arbitrary multi-mode states. And then, we evaluate the control power through quantum nonlocality in continuous variable controlled quantum teleportation via a 3-mode GHZ-type entangled coherent state as channel. The results show that the control power of continuous variable quantum networks is a monotonically increasing function of genuine tripartite nonlocality. This quantitative dependence of control power on quantum nonlocality remains robust even with decoherence. The advantages of the MK inequality are simplicity in computation and scalability into arbitrary multi-mode channels. In addition, maximal violation of the MK inequality can be achieved more easily in the experiment. Our work proves that, compared with the Bell−Mermin inequality, the MK inequality performs better in experimental measurements of complete control power; compared with the Svetlichny inequality, the MK inequality avoids negative and unreasonable control power when inequalities exceed the classical upper bound. Therefore, the MK inequality is found to be a more reliable tool to reveal the quantum nonlocality in multipartite systems. This work illuminates the important application of nonlocality in multipartite continuous variable quantum communications and is of significance for the construction of practical quantum protocols.
Controlled quantum teleportation is an important extension of multipartite quantum teleportation, which plays an indispensable role in building quantum networks. Compared with discrete variable counterparts, continuous variable controlled quantum teleportation can generate entanglement deterministically and exhibit higher superiority of the supervisor's authority. Here, we define a measure to quantify the control power in continuous variable controlled quantum teleportation via Greenberger-Horne-Zeilinger-type entangled coherent state channels. Our results show that control power in continuous variable controlled quantum teleportation increases with the mean photon number of coherent states. Its upper bound is 1/2, which exceeds the upper bound in discrete variable controlled quantum teleportation (1/3). The robustness of the protocol is analyzed with photon absorption. The results show that the improving ability of the control power will descend by the increasing photon loss, with the upper bound unchanged and robust. Our results illuminate the role of control power in multipartite continuous variable quantum information processing and provide a criterion for evaluating the quality of quantum communication networks.
Experimental demonstration of entanglement needs to have a precise control of experimentalist over the system on which the measurements are performed as prescribed by an appropriate entanglement witness. To avoid such trust problem, recently device-independent entanglement witnesses (\emph{DIEW}s) for genuine tripartite entanglement have been proposed where witnesses are capable of testing genuine entanglement without precise description of Hilbert space dimension and measured operators i.e apparatus are treated as black boxes. Here we design a protocol for enhancing the possibility of identifying genuine tripartite entanglement in a device independent manner. We consider three mixed tripartite quantum states none of whose genuine entanglement can be detected by applying standard \emph{DIEW}s, but their genuine tripartite entanglement can be detected by applying the same when distributed in some suitable entanglement swapping network.
The phenomenal progress in quantum technologies over the past decades has laid the groundwork for the construction of quantum networks, which will channel the power of quantum theory to guarantee secure and efficient communication, computation, and much more. This thesis studies the notion of trust in quantum networks. In our information age, protecting the security or anonymity of data is a key requirement. We investigate certain protocols that are fundamental to the operation and applications of quantum networks, and propose ways to test and analyse their security, in spite of adversarial intervention. Our focus is on practical methods of verifying the untrusted components, which could be incorporated into realistic networks in the near future. To begin, we propose a protocol for authenticated communication of quantum messages, by verifying the entanglement required for quantum teleportation in an experimentally feasible way. We model the performance of our scheme in the presence of noise. Furthermore, we explore such an authenticated teleportation in the one-sided device-independent scenario, where some devices used for verification may be corrupted. We derive error-tolerant self- testing bounds and extend our results to a realistic experimental setting, demonstrating the compatibility of our protocol with state-of-the-art technology. We then study anonymity, an essential feature for communication across networks. Combining the power of classical and quantum subroutines, we build a practical protocol for anonymous communication of quantum messages, without the need to trust the players in our network, their computational power, or the entanglement they share. We end by considering the verification of graph states distributed across a network of possibly dishonest players, applying our scheme to specific graph states that are central to quantum communication and computation schemes.
In distributed quantum computing, quantum networks provide a potential infrastructure for long-range quantum information processing. Controlled quantum teleportation (CQT) is a key practically relevant protocol that can connect two parties on a network and enables a third party, the controller to allow or abort the secure teleportation of an arbitrary single-qubit state between the two parties. We investigate the robustness of a three-qubit GHZ resource under bit-flip, phase-flip, depolarizing, and amplitude-damping noise. Using the Kraus-operator formalism, we characterize the noisy resource through multipartite quantum discord, genuine multipartite concurrence (GMC), localizable entanglement (LE), and CQT fidelity. We also outline a proof-of-concept photonic implementation for preparing the three-qubit GHZ resource and realizing the CQT protocol, which could enable experimental investigation of the effects of noise. Our results show that bit-flip and amplitude-damping noise generally preserve useful mutipartite quantum correlations over broader noise parameter ranges. Interestingly, multipartite discord exhibits freezing under bit-flip noise over a finite parameter regime. Moreover, discord can persist beyond the sudden death of genuine multipartite entanglement, revealing the distinct robustness of nonclassical correlations. We further demonstrate that CQT fidelity which characterizes the performance of CQT can exceed the classical threshold even after GMC vanishes, while LE more closely reflects the operational usefulness of the noisy resource. These findings highlight the complementary roles of quantum correlations and entanglement in assessing the resilience of GHZ-based protocols.